Complete Water Services Article for the American Conifer Society

Complete Water Services Article for the American Conifer Society

“Water, water everywhere / Nor a drop to drink.” With only three percent of Earth’s water being freshwater, and only 12% of that as surface water, available groundwater, or other accessible water, that old saying from Samuel Taylor Coleridge’s poem The Rime of the Ancient Mariner speaks volumes.

“Civilization has been a permanent dialogue between human beings and water.” – Paolo Lugari

Harvesting rain is a practice that has been around for centuries. Cisterns and other rain harvesting systems are widely used in Europe, Africa, Australia, India, the Bahamas, and countless remote countries. Many individuals in these nations rely exclusively on rainfall for their day-to-day existence. Here in the United States, we, too, can successfully harvest rainwater to meet many of our needs.

When someone mentions rainwater harvesting (RWH), mental images of storage tanks, piping, hoses, etc., may come to mind. This is only one type of rainwater harvesting–active harvesting–and it works wonderfully well. However, there is another type called passive harvesting, which allows the soil to act as the “storage tank.” In this article, we will highlight both types of rainwater harvesting.

Value of RWH

The value of RWH cannot be overly emphasized. RWH can supplement potable (in some areas) and non-potable water demands, reduce run-off, reduce flooding, control erosion, manage stormwater quantity, increase water infiltration, reduce potable water costs, increase property values, and enhance environmental qualities.

Rainwater harvesting can be employed on a small or large scale, from a simple rain barrel, to an extensive multipurpose collection system. What is great about rainwater harvesting is that it does not need to be an elaborate or expensive proposition. It can be as simple as directing roof runoff to a swell or depression.

Types of RWH

The type of RWH you employ depends on the water needs, type of water usage, site location, amount of rainfall, drainage pattern, soil type, soil structure, etc. The following definitions are from the American Rainwater Catchment Systems Association (ARCSA)1:

Active Rainwater Harvesting: The collection and stor- age of rainwater in a container for later beneficial use.

Active Rainwater Harvesting System: The combined components that enable catchment, conveyance, removal, tank storage, and distribution of rainwater runoff for later beneficial use, including any needed pressurization and treatment.

Passive Rainwater Harvesting: The collection and infiltration of rainwa- ter into the ground for beneficial use, without intermediate storage in a tank.

Passive Rainwater Harvesting System: The combined components, including the passive infiltration structure, conveyance from rooftops, piping, rock, mulch, and other materials that enable the capture and infiltration of rainwater into the ground without intermediate storage in a tank.

Most RWH systems employ both types, an integrated system of active and passive rainwater harvesting. Needless to say, there are several ways to design an active RWH system. The possibilities are truly endless.

Basic Sizing of RWH

Calculate RWH Volume: A general rule-of-thumb is that you can harvest around 620 gallons of rainwater during a 1″ rain event per 1,000 square feet of roof area. Many calculators are online to assist with calculating the volume of rainwater available in your area.2
Determine Monthly Water Demand: With the end use(s) in mind, estimate the total amount of water that you will use for each month of the year. You can find several charts on the Internet to help estimate the water required per use/per person/per area,2 etc.; however, the demand will be based on your particular needs.

Passive RWH

Passive RWH is the most common way of using harvested rainwater. It can be the simplest and easiest way, too, because systems can be installed without pumps and the end use usually does not require in- tense treatment. The axiom for passive RWH is:


Slowing the flow of rainwater makes it easier to manage and reduces detrimental effects, such as erosion. Routing the flow in the desired direction provides an opportunity for filtering, infiltration, and conveyance to areas of use. Growing means guiding the water directly to the root zones of the plants to reduce water usage and evaporative losses and then letting nature handle the rest.

Passive RWH structures can be constructed in count- less shapes, sizes, and configurations to accommodate the lay of the site and to intercept the flow from rooftops, hardscapes, impervious surfaces, land- scapes, and slopes. Passive structures can retain a significant amount of rainwater and come in many types:

  • A basin, with or without berms or multiple basins Waffle gardens: sunken garden beds that look similar to the indentations in waffles
  • Rain gardens: amended beds for increased wa- ter-holding capacity
  • Contour swales, with or without berms
  • Contour swales inside larger drainage basins
  • Wattle swales: long sausage-shaped products, often filled with straw, used to slow the flow rate and detain debris and sediment
  • French drains: underground structures (e.g., rock- filled trenches or corrugated drainage piping) so that water can drain and infiltrate adjacent soils Rain barrels
  • Curb cuts to help disperse water from impervious areas
  • Permeable paving and porous concrete

Most passive RWH structures are hidden behind a cover of plants and disappear from view but continue working nonetheless.

General Approaches to Passive RWH

Site-specific factors for passive RWH sizing and design include

  1. Goals for the site such as controlling erosion, supporting vegetation and plantings, and reducing runoff
  2. The amount of water needed by new and existing plantings
  3. The size of available catchment areas
  4. Local rainfall averages and maximums
  5. Runoff coefficients for the different catchment surfaces (charts and calculators are available on many websites3)
  6. Infiltration rates based on site-specific soil types and conditions
  7. Depth of usable soils above non-infiltration zones such as hardpan, clay lenses, high groundwater table, bedrock, etc.
  8. The lay of the land in relation to how and where the flow will be routed
  9. Local regulations on the maximum depth of impounded water

Strategies for a Passive RWH System

Effective strategies for a passive RWH system that focus on efficient rainwater utilization and landscaping practices include

  1. Leave as many native trees or plants as possible and work these into the overall RWH plan
  2. Remove vegetation and reshape the topography to direct roof and surface runoff to the new infiltration areas constructed
  3. Meet outdoor water demand for existing and new plants using passive RWH to the greatest extent possible or practical
  4. Replace grass or other high-water-demand vegetation with native, low-water-use and low-maintenance trees and shrubs to provide shade, cooling, food, and wildlife habitat
  5. Be cognizant of sun angles, which vary with latitude, when planting trees and shrubs. These can be placed to allow the low angle of the sun to warm buildings during cold months while shading buildings during the warm months
  6. Place new planting areas adjacent to or near hardscape areas that can provide runoff watering
  7. Calculate basin volumes and dimensions (or other containment structures) based on direct rainfall plus the runoff that will flow into them
  8. Construct overflow structures to direct and convey excess water from passive RWH areas to other areas for beneficial use

Rain Barrels

Rain barrels are one of the easiest and most inexpensive ways to collect rainwater for future use. From utilitarian to highly decorative, rain barrels come in various colors, sizes, and styles so that they can be incorporat- ed seamlessly into your landscape.4

When selecting a rain barrel, there are various factors to consider. Volumes of barrels vary from 35 gallons to 120 gallons. Many have interconnecting nozzles on the sides so that barrels can be manifolded together. Most are made from heavy-duty plastic, providing UV protection and making them durable. Barrels should have a screen across the inlet to keep out debris and insects, particularly mosquitoes. Barrels should have an overflow nozzle at the top and a spigot (or another type of outlet) at the bottom. Ensure the spigot is high enough if a watering can is to be placed underneath. The barrel may need to be placed on a stand.

Active RWH

Active RWH systems have become increasingly relevant as populations and water demands have drastically increased. Shortages of conventional water supplies, extended droughts, and groundwater and surface water depletion are just some of the current and future challenges. Even in the most arid climates, there is sufficient rainfall for active RWH to help meet a wide range of water requirements.

Active systems can utilize everything from small barrels to large, interconnected tanks; from underground collection systems to lined ponds. Active systems provide many benefits:

  • Maximize the use of free, local rainfall
  • Reduce demands from potable, surface water, and water well sources
  • Provide stored water for use during drought and use restrictions
  • Provide safe potable water when no other source is available
  • Supply water during peak demand periods
  • Provide water for firefighting and other non-potable uses

Active RWH systems must safely capture, collect, convey, filter debris, store, pump, and treat (filtration, disinfection, etc.) rainwater for the intended quantity, quality, and use. Components include

  • Catchment surfaces (e.g., roofs, parking lots, im- pervious surfaces)
  • First flush diverter
  • Conveyance to tank or other storage element
  • Debris filtering and removal
  • Storage vessel or system (barrels, totes, tanks, cisterns, ponds, etc.)
  • Piping to and from storage vessel or system
  • Pumps and pressurization systems (if required)
  • Post-storage filtration and disinfection (if required by end use)
  • Irrigation system (if required by end use)

General Approaches to Active RWH

To optimize the effectiveness of an Active RWH system, consider the following general approaches:

  1. Ensure that the gutters, downspouts, and inflow pipes are sized sufficiently to handle the maximum amount of rainfall
  2. Ensure that the tank overflow piping has a capacity equal to, or preferably larger, than the inflow piping
  3. Ensure overflow from underground tanks has a safe point of discharge, preferably for beneficial use
  4. Direct any overflow to a location for beneficial use
  5. Design the system to yield high-quality water. Be cautious of toxic materials, such as harvesting from areas that have pesticides and herbicides applied, vehicle drippings, chemical storage areas, railroad ties, landscape timbers, etc.
  6. Use components rated for use in potable water systems if the rainwater is to be used as drinkable water or may be used as such in the future
  7. Use calming influent devices to minimize sediment disturbance at the bottom of the tank, for example, install outflow piping four inches or more above the bottom of the tank, or use a floating outflow device to minimize sediment disturbance
  8. Block sunlight to prevent algae growth
  9. Install screens on all ports to eliminate insects, birds, and vermin
  10. Install self-cleaning or minimal maintenance pre-filters to enhance water quality. Locate these in easy-access locations
  11. Install first-flush devices in low-maintenance locations
  12. Maintain access around tanks (rule-of-thumb is three feet) and inside tanks for inspection, cleaning, and repair
  13. Secure tanks with lockable lids for safety and to prevent unwanted entry
  14. Vent tanks to allow airflow for changing water levels to keep the tank from collapsing
  15. Use gravity flow where feasible for energy-free water delivery

Strategies for an Active RWH System

To optimize the functionality of an Active RWH System, consider implementing the following strategic measures:

  • Select a tank location that is appropriate for the catchment surface and is in the proximity of the end use
  • Determine the type of conveyance based on the site climate: dry conveyance (where the convey- ance system is designed to drain all the rainwater directly into the tank and remain dry between rainfall events) can be used in hot or cold climate areas and wet conveyance (where the conveyance system is designed to hold standing water between rain events) is susceptible to freezing in colder climates
  • Select a storage tank with dimensions based on the specific site constraints, required capacity, catchment surface height (e.g., roof overhang height), prefiltration devices, tank materials, etc.
  • Select a water treatment system regime based on the quality of water required by the end use
  • If used to supplement potable water, ensure that the required backflow prevention devices are in- stalled per the local code


Please be aware that the legal right to harvest and use rainwater varies depending on state and local laws, regulations, practices, and codes5. This variation arises from the complexities of water rights and allocations. It is essential to consult with your state and local agencies to understand the specific regulations and requirements that apply to rainwater harvesting in your area6. Additionally, it is advisable to investigate any relevant planning, building, and installation codes and regulations before initiating any rainwater harvesting projects to ensure compliance.

It has never been more important to work for environmental sustainability. Rainwater harvesting systems provide distributed stormwater runoff containment while simultaneously storing water that can be used for irrigation, landscaping, flushing toilets, washing clothes, washing cars, and pressure washing, or it can be purified for use as everyday drinking water. Harvested rainwater has many diverse uses, but its impact is the same-water conservation.

Active and passive RWH tactics, whether used separately or together in a comprehensive plan, can turn stormwater problems into water supply assets. From large-scale projects or a single rain barrel, RWH practices can supplement or entirely supply high-quality water now and into the future.

Small steps can make a huge impact.

“If there is magic on this planet, it is contained in water.” – Loran Eiseley

Further Reading

  1. American Rainwater Catchment Systems Asso- ciation (ARCSA), Rainwater Harvesting Manual, 1st Edition Second Printing, 2015.
  2. Example of Comprehensive Calculators: Depart- ment of Energy, Texas A&M Agrilife Extension,
  3. MyMathTables Rainwater Runoff Calculator, https://www.mymath weather/rainwater-runoff-using-rational method.html. Runoff Coefficient Fact Sheet
  4. The Spruce. The 9 Best Rain Barrels of 2023.
  5. Federal Energy Management Program, Rainwa- ter Harvesting Regulations Map,; Pacific Northwest National Laboratory, Rainwater Harvesting State Regulations and Technical Resources, PNNL-24347 Rev 1, June 2019. publications/external/technical_reports/PNNL-24347Rev.1.pdf